Strength and stiffness of cellular foamed materials

Abstract

The use of cellular foams as a core material in light-weight optical and structural systems is of considerable interest. Research and development of these systems, however, have been hampered by the lack of material property data and uncertainty in the use of various suggested material characterizations and the associated constants of proportionality. ASTM standards were researched and, for the most part, found inadequate for testing cellular foam materials. The compression, tension and shear test methods developed are presented, as well as the results from physical tests on closed-cell SXATM foam specimens. Based on the test results, material characterizations are presented. Additionally, a parametric study was performed to investigate the behavior of open and closed-cell foams. Twenty-one (21) finite element models were built and seventy (70) analyses were performed to study the effects of cell geometry. Based on the FEA results, material characterizations are presented for the cubic array and the tetrakaidecahedron geometry. The FEA results are compared with the characterizations proposed by Gibson and Ashby and the test results. The validity of the scaling laws are confirmed; however, the proposed constants of proportionality overestimate the modulii a minimum of 50%. New constants are presented for both open-cell and closed-cell foams, as well as additional insights into the effects of cell shape on Poisson's ratio.